The present invention relates generally to a gearshift mechanism for use with a vehicle transmission. More particularly, the present invention relates to a spring biased self-centering shifter assembly for use with a multi-speed manual transmission of a vehicle for shifting the manual transmission between a plurality of ratio gear positions.
As is known, manual transmissions are conventionally equipped with a shifter assembly for permitting a vehicle operator to selectively shift between various forward ratio gears and a reverse gear. The shifter assembly generally includes a tower housing secured to an exterior surface of the transmission casing. A shift lever is pivotally mounted to the tower housing and operably coupled to a gearshift mechanism located within the transmission casing.
One type of shifter assembly well known in the art is referred to as a "drop-in" type shifter. Drop-in type shifters normally include a shift mechanism formed to include a fulcrum ball which is pivotally received with a socket formed in a base. The shift lever extends from the bottom of the base into the transmission for changing the drive ratio of the transmission in response to operator control of the shift lever. The base is positioned over an aperture in the transmission housing and secured to the top of a transmission with bolts.
A longstanding problem associated with conventional shifter assemblies, including drop-in type shifters, is the propagation of vibration from the power transfer unit of a vehicle to the shift lever. Many attempts have been previously made to eliminate such vibration and the undesirable noise generated therefrom. For example, is it known to incorporate a vibrational dampening bushing between the lower end of the shift lever and its interconnection to an associated gearshift mechanism. A similar manner of vibrational dampening is disclosed in U.S. Pat. No. 3,780,596 to Takahashi et al., where a resilient material is incorporated between the fulcrum ball and its support surface. In these arrangements, however, the quality of operator feel upon selective shifting on the shift lever is often sacrificed.
It is also known to reduce the propagation of undesirable vibrations to a shift lever by continuously biasing the shift lever into a neutral position or neutral plane. For example, U.S. Pat. Nos. 4,333,360 and 4,581,951 disclose arrangements in which the shift lever is biased by a pair of helical compression springs. U.S. Pat. No. 2,853,895 to Bixby discloses a transmission shift lever biased by arcuate spring segments vertically mounted at opposite ends of a pin. U.S. Pat. No. 4,569,245 to Feldt et al. discloses a shifter arrangement incorporating a single flat washer-like spring for biasing a shift lever.
The prior art attempts to utilize spring biasing characteristics to mitigate propagation of power train vibrations involve disadvantages primarily related to the expense of manufacture. In addition thereto, not only are the components relatively expensive, assembly techniques have proven to be both difficult and time consuming. In some of the prior devices, preloading of the biasing mechanism is required prior to installation. In other prior devices, the location of the biasing mechanism prevents the shifter assembly from being quickly and easily "dropped" into connection with an associated gearshift mechanism. Many prior art devices include numerous metal components which are known to readily transmit noise and vibrations.
While conventional shift assemblies have proven to be commercially acceptable, each is associated with disadvantages and/or inherent limitations, some of which have been discussed above. Accordingly, a need exists for an improved shifter assembly which is less costly to produce, reduces the number of components to manufacture and assemble, reduces noise and vibrations, has an improved operator feel, yet is reliable and easy to manufacture and assemble.